<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        *{
            margin: 0;
            padding: 0;
            box-sizing: border-box;
            
        }
        body{
            height: 200vh;
            
        }
        .tou{
             position: fixed;
             top: 0;
             left: 0;
             padding: 25px 100px;
             width: 100%;
             display: flex;
             justify-content: space-between;
             align-items: center;
            transition:  0.5s;
         }
        .logo{
             position: relative;
             font-size: 22px;
             font-weight: 900;
             letter-spacing: 1px;
             color: rgb(28, 36, 148);
         }
         .logo::before{
            content: '';
            position: absolute;
            left: -50px;
            top: -15px;
            width: 50px;
            height: 50px;
            background-image: url(logo.png);
            background-size: 100%;
         }
         .biao{
             position: relative;
             display: flex;
             justify-content: center;
             align-content: center;
            list-style: none;
            
         }
        .biao li{
             position: relative;
         }
        .biao a{
             position: relative;
             margin: 0 10px;
             font-size: 18px;
             font-family: 'fangsong';
             font-weight: bold;
             color: rgb(28, 36, 148);
             text-decoration: none;

         }
          
        .bian{
            padding: 15px 100px;
            background-color: rgb(71, 105, 219);
        }
        .bian .logo,.tou.bian a{
            color: rgb(252, 247, 247);
        }
       /*  背景图样式 */
        .bjimg {
      position: fixed;
      top: 0;
      left: 0;
      width: 100%;
      height: 100%;
      min-width: 1000px;
      z-index: -10;
      zoom: 1;
      background-color: #fff;
      background-image: url(11.jpg) ;
      background-repeat: no-repeat;
      background-size: cover;
      -webkit-background-size: cover;
      -o-background-size: cover;
      background-position: center 0;
    }

    </style>
</head>
<body>
    <!-- 背景图 -->
    <div class="bjimg"></div>

   <!--  导航栏 -->
    <div class="tou">
        <sapn class="logo"> 北极光。</sapn>
        <ul class="biao">
        <li><a href="#"><a href="#">主页</a></li>
        <li><a href="#">个人简介</a></li>
        <li><a href="#">文章</a></li>
        <li><a href="#">留言版</a></li>
        <li><a href="#">友链</a></li>
        </ul>
    </div>
    <script>
        window.addEventListener('scroll',function(){
            let tou = document.querySelector('.tou');
            
           
           /*  tou.classList.toggle("bian",window.scrollY>0); */
           if(window.scrollY>0)
            {
                tou.classList.add("bian");
            }else{
                tou.classList.remove("bian");
            }
        })
    </script>
</body>
</html>
